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Python | Find maximum length sub-list in a nested list

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  • Difficulty Level : Medium
  • Last Updated : 19 Feb, 2019

Given a list of lists, write a Python program to find the list with maximum length. The output should be in the form (list, list_length).

Examples:

Input : [['A'], ['A', 'B'], ['A', 'B', 'C']]
Output : (['A', 'B', 'C'], 3)

Input : [[1, 2, 3, 9, 4], [5], [3, 8], [2]]
Output : ([1, 2, 3, 9, 4], 5)

 
Let’s discuss different approaches to solve this problem.

Approach #1 : Using for loop (Naive)
This is a brute force method in which we iterate through each list item(list) and find the list with maximum length. Similarly, we use the for loop to find length of each list and output the maximum length.




# Python3 program to Find maximum 
# length list in a nested list
  
def FindMaxLength(lst):
    maxList = max((x) for x in lst)
    maxLength = max(len(x) for x in lst )
  
    return maxList, maxLength
      
# Driver Code
lst = [['A'], ['A', 'B'], ['A', 'B', 'C']]
print(FindMaxLength(lst))
Output:
(['A', 'B', 'C'], 3)

 
Approach #2 : Using map
In this method we use Python map function to iterate over the inner lists to create a list of lengths, then get the maximum with max function.




# Python3 program to Find maximum 
# length list in a nested list
  
def FindMaxLength(lst):
    maxList = max(lst, key = len)
    maxLength = max(map(len, lst))
      
    return maxList, maxLength
  
# Driver Code
lst = [['A'], ['A', 'B'], ['A', 'B', 'C'], ]
print(FindMaxLength(lst))
Output:
(['A', 'B', 'C'], 3)

 
Approach #3 : Using lambda operator
One more method in Python to find the longest length list is the lambda operator. It is used for creating small, one-time and anonymous function objects in Python. Here we pass a variable i as argument in the len(i) expression and find the maximum length.




# Python3 program to Find maximum 
# length list in a nested list
  
def FindMaxLength(lst):
    maxList = max(lst, key = lambda i: len(i))
    maxLength = len(maxList)
      
    return maxList, maxLength
# Driver Code
lst = [['A'], ['A', 'B'], ['A', 'B', 'C']]
print(FindMaxLength(lst))
Output:
(['A', 'B', 'C'], 3)

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